1. Field of the Invention
The present invention relates generally to satellite video systems, and in particular, to a method, apparatus, and article of manufacture for frequency drift estimation in satellite outdoor unit systems.
2. Description of the Related Art
Satellite broadcasting of communications signals has become commonplace. Satellite distribution of commercial signals for use in television programming currently utilizes multiple feedhorns on a single Outdoor Unit (ODU) which supply signals to up to eight Integrated Receiver/Decoders (IRDs), e.g., set top boxes, on separate cables from a multiswitch.
FIG. 1 illustrates a typical satellite-based broadcast system of the related art.
System 100 uses signals sent from Satellite A (SatA) 102, Satellite B (SatB) 104, and Satellite C (SatC) 106 that are directly broadcast to an Outdoor Unit (ODU) 108 that is typically attached to the outside of a house 110. ODU 108 receives these signals and sends the received signals to IRD 112, which decodes the signals and separates the signals into viewer channels, which are then passed to monitor 114 for viewing by a user. There can be more than one satellite transmitting from each orbital location (slot). The orbital slots are typically designated by their longitude, so, for example, a satellite 102 located in the orbital slot at 101 degrees West Longitude (WL) is usually referred to as transmitting from “101.”
Satellite uplink signals 116 are transmitted by one or more uplink facilities 118 to the satellites 102-106 that are typically in geosynchronous orbit. Satellites 102-106 amplify and rebroadcast the uplink signals 116, through transponders located on the satellite, as downlink signals 120. Depending on the satellite 102-106 antenna pattern, the downlink signals 120 are directed towards geographic areas for reception by the ODU 108.
Each satellite 102-106 broadcasts downlink signals 120 in typically thirty-two (32) different frequencies, which are licensed to various users for broadcasting of programming, which can be audio, video, or data signals, or any combination. These signals are typically located in the Ku-band of frequencies, i.e., 11-18 GHz, but can also be broadcast in the Ka-band of frequencies, i.e., 18-40 GHz, but typically 20-30 GHz.
Within ODU 108, the downlink signals 120 are downconverted to lower frequencies using an oscillator and a mixer. Typically, the oscillator is a Dielectric Resonant Oscillator (DRO). If the DRO frequency drifts, the downconversion of the downlink signals 120 drifts as well, which makes processing of such downconverted signals more difficult.
Further, as satellites 102-106 broadcast additional services and additional channels to viewers, as well as additional satellite signals present in such bandwidths, it will be more efficient to monitor and, if necessary, correct drifts in the DRO frequency.